Second Soil

Spilling the dirt on alternative growing mediums for indoor plants.

New indoor plants often just get planted straight into good old potting soil – or whichever planting mix we find at the local nursery we purchased it from. 

For most, this is a good option, but you might also find you are limited in space, having only a few shelves on top of which resting a heavy medium like potting soil might not be the best idea.  Perhaps you’re wanting to avoid soil borne pests or looking for a different way to propagate your house plants… Hello, do come in and sit down, I’ve got you covered plant parents. 

When reconsidering your medium, there are a few alternatives in which to home your new plant. Alternative soil does have its drawbacks and advantages, and sometimes is very costly. 

So, like any good side piece (I mean, second soil) it needs to meet your needs, whilst not giving you the same issues as the original, as it will be ever-present in your life. 

Sphagnum moss

There are two types of sphagnum you might encounter, the first being sphagnum peat. This is the remnants of live moss that have broken down with some animal remains, and is very high in nutrients. It is a great soil additive for large-scale applications to assist in water retention and adding organic matter to poor quality soils. 

The second is Sphagnum moss, which is farmed and sourced from the northern hemisphere wetlands and bogs. It is the dried remains of the living top layer. It has a neutral pH, with little organics and the ability to retain water very effectively. This makes it an excellent medium for plants that require moist roots along with high humidity. Orchids are often grown in sphagnum moss and it’s ideal for kokedama. 

An additional use for moss is to air root aroids and to propagate them. A drawback of this medium is that it is costly and unfortunately not a renewable resource.


LECA is a very strange anomaly; it looks too pebbly to be a growing medium and feels too light to actually retain anything. In that, it’s one of the best growing or propagating mediums. LECA is an acronym for Lightweight Expanded Clay Aggregate. Simply put, it’s baked clay balls that expand when soaked in water. The clay is fired once, which means it won’t become a muddy mess, but is extremely porous. The ability to absorb water is a great benefit as it is able to release water at a slow rate – as needed by the plants. 

A great growing hack is to add some liquid fertiliser when you soak them, so they release the nutrients and water to the roots. The large size of each clay ball allows for optimum airflow around the roots too. Personally, I’ve had great success with getting stubborn water cuttings to root rapidly in LECA. You will be blown away by the number of roots you get in this medium. 

One of my personal favourite attributes of this medium is that it is 100% reusable. Simply remove your very well rooted plant when you replant it. Take your clay balls, rinse out all debris, boil in some water to sterilize, rinse and they are as good as new. That’s very LECA even though the price tag sometimes isn’t.

Coir or Coco Peat

Coir is a by-product of coconuts. It’s the pith between the long fibrous hairs of the outer husks. The coir pith gets washed, heat-treated, sieved to remove large particles and graded. Very often it is compressed into blocks or bricks, which need to be soaked before using. You may also find bags or bales of coir. This produces a sterile growing medium that has a great water retention ability. 

If you’ve ever bought one of these coir bricks you will be surprised at how much water it takes to rehydrate this medium; a 5l bucket of water is easily absorbed through a 2kg brick. 

The drawback of this product is that it has almost no available nutrients for plants and can dry out rapidly in a warm space. When growers use this as a medium, they often use it in conjunction with a very heavy liquid fertilizer program to ensure proper growth. It is a very lightweight medium which means you can transport more plants, reducing the carbon footprint, and that’s pretty p(n)eat.


Imagine you live in Salem in the 1600s… Because this growing medium is witchcraft! Rockwool is melted rock that is spun into fibres that become something similar to fibreglass, which is then compacted into little blocks or slabs. I know, my foundation was just rocked too. 

This medium has a great water retention ability (insert liquid fertilizer hack here) and due to being so fibrous, it is easily adjusted to any size container you require. Transplanting simply requires placing some more rockwool in the larger container and placing your old plant into it. A drawback, yes, just like witchcraft, this medium is dangerous. When using it, use a face mask as the fibres can cause respiratory irritation. 

These are simply a few alternative growing mediums. My professional recommendation is to use them during the propagation process and for young plants. Once your plants reach teenage years you’re going to have to give them some space (typical teenagers) and they will appreciate a good homemade indoor potting mix, even though they might still slam the door and yell that no one understands them. 

Mark Mac Hattie

Landscape designer

Contours Design Studio